The subject invention relates to a sinker drill or down-the hole rock drill using a percussion drill bit provided at the lower end of the drill rod, the latter being rotatably driven from an above-the-ground driving motor.
Several kinds of drilling machines of this kind are already known. In accordance with one type of such drills, an hydraulically or pneumatically operated percussion machine is used at the upper end of the drill rod. The hammer blows must propagate over the full length of the entire drill rod which consists of a number of sections that must be joined together, and consequently the impact on the drill bit is considerably reduced. To remedy this drawback, a drilling machine has been designed, wherein the percussion machine is positioned at the lower end of the drill rod, whereby the hammer blows will hit the drill bit directly. Hitherto, the only possibility to drive percussion machines of this kind has been with the aid of compressed air or hydro-electrically from units positioned above the ground. However, when the drill holes are large, in the order of between 0.5 to 1 meter in diameter or more, percussion machines driven pneumatically or hydro-electrically via a turbine give an effect (power) that is too small to make their operation economical.